| The main research work is described as follows:1. Fabrication of Poly (aspartic acid)-Nanogold Modified Electrode and Its Application for Simultaneous Determination of dopamine, ascorbic acid, and uric acidA nanostructured polymer film incorporated gold nanoparticles modified electrode was fabricated. The fabrication process involved a previous electropolymerization of aspartic acid and followed by the eletrodeposition of gold nanoparticles on the glassy carbon electrode. The resulting poly (aspartic acid)-nanogold modified electrode (PAA-nano-Au/GCE) was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The modified electrode combines the high sensitivity of gold nanoparticals and the selectivity of PAA, this PAA-nano-Au/GCE has significant electrocatalytic activity towards the oxidation reactions of DA, AA and UA, and their oxidation peaks move to about0.2V,0.0V and0.35V, respectively. Simultaneous determination of DA, AA, and UA were studied by voltammetry. The linear range of5.0×10-7-1.0×10-4M for DA,5.0×10-6-2.0×10-3M for AA and5.0×10-6-1.0×10-3M for UA was obtained. The detection limit was calculated for DA, AA and UA as being6.5×10-8M,5.6×10-7M and3.0×10-7M, respectively (S/N=3). The practical application of the present modified electrode was demonstrated by the determination of DA, AA and UA in calf serum and fetal calf serum samples.2. Determination of dopamine with improved sensitivity by exploiting an accumulation effect at a nano-gold electrode modified with poly (sulfosalicylic acid)We describe a glassy carbon electrode modified with nano-gold and a film of poly (sulfosalicylic acid) that was obtained by electropolymerization of sulfosalicylic acid and then eletrodeposition of gold nanoparticles. The electrochemical characteristics of the electrode were investigated by using (a) the anionic hexacyanoferrate, and (b) the cationic ruthenium-trisbipyridyl systems as redox probes. The electrode displayed selective and enhanced electroanalytical response towards dopamine (DA), obviously because DA (which is cationic) is accumulated at the electrode, while anions such as ascorbic acid (AA) do not and in fact are being repelled. A2000-fold molar excess of AA is tolerated after a120-s accumulation time followed by stripping detection at pH6.5. Response is linear with the concentration of DA in the range from0.05to5μM, and the detection limit is7nM (at an S/N of3) even in the presence of100M AA. Experimental was also carried on determining dopamine hydrochloride injection samples with satisfactory results.3. Electrogenerated chemiluminescence sensor for glutathione with Ru(bpy)32+-doped silica nanoparticles modified electrodeThe experiments using reverse microemulsion method for synthesis of the nanoparticles of tris(2,2-bipyridyl)ruthenium(Ⅱ)(Ru(bpy)32+)-doped silica nanoparticles (RuDSNPs). These uniform RuDSNPs were characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM), about58±4nm in diameter. The Ru(bpy)32+encapsulation interior maintained its high electron-activity, while the exterior nano-silica surface prevented the mediator from leaching out into the aqueous solution due to the electrostatic interaction, and showed high biocompability. A electrogenerated chemiluminescence (ECL) sensor for glutathione was developed based on tris(2,2-bipyridyl)ruthenium(Ⅱ)(Ru(bpy)32+)-doped silica nanoparticles (RuDSNPs) modified gold electrode. With such unique immobilization method, it could greatly enhance the ECL response and result in the increased sensitivity. The ECL analytical performances of this ECL sensor for glutathione based on its decrease ECL emission of Ru(bpy)32+were investigated in details. Under the optimum condition, the decreased ECL intensity was linear with the glutathione concentration in the range of1×10-9to1×10-5M (R=0.9978). The method was successfully applied to the determination of glutathione in pharmaceutical samples with satisfactory results. The as-prepared ECL sensor for the determination of glutathione displayed good sensitivity and stability.4. Voltammetric sensor for NADH based on a glassy carbon electrode modified with grapheneThe electrochemical reduction from graphene oxide (GO) to graphene (GR) could overcome a series of drawbacks of the conventional chemical reduction method, such as the process is complex, time-consuming steps, and the reducing agent used may cause environmental pollution. We report on a voltammetric sensor for NADH that is based on a glassy carbon electrode modified with the graphene (GR). The results indicated that this electrochemical sensing interface has the advantages, such as quick electron-transferrate, avoidance of electrode fouling, highly sensitive and stable amperometric sensing for NADH. The two dimensional structure and large specific surface area of GR should be responsible for electrocatalytic behavior. The electrochemical sensor based on GR exhibited wide dynamic range from10to1000μM, low detection limit of1.3μmol/L, very high sensitivity of8.9μA mM-1, and good stability for the detection of NADH. From the results of electrochemical investigation, graphene with a favorable electrochemical activity could be an advanced carbon electrode materials for the design of electrochemical sensors and biosensors. |
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